1. Fields of the Invention
The present invention generally relates to Synchronous Peer to Peer Remote Copy (SRC) protocol generally, and more particularly, the present invention relates to migrating a SRC (i.e., mirroring between a primary storage device and a secondary storage device) from a backend storage subsystem (i.e., un-virtualized storage platform; e.g., IBM® DS8000) to a storage virtualization appliance (e.g., IBM® San Volume Controller).
2. Description of the Prior Art
The Peer to Peer Remote Copy (PPRC) is a protocol to mirror a primary storage device located at a primary site to a secondary storage device located at a remote site. Synchronous PPRC (SRC) causes each write to the primary storage device to be performed to the secondary storage device as well, and the I/O (Input/Output) is only considered complete when update to both primary and secondary have completed. In some applications, a customer may want to migrate his/her SRC relationship (i.e., an instance of a SRC between a primary storage device and a secondary storage device) from a backend storage subsystem (e.g., IBM® DS8000, IBM® DS4000, EMC® Symmetrix®, EMC® CLARiiON®, etc.) to a storage virtualization appliance (e.g., IBM® San Volume Controller and the like). Currently, it is not possible to perform this migration without an interruption on a host device (i.e., a server) or losing data consistency (i.e., data is consistent if all interrelated data (e.g., a group of data set) have a same instance (e.g., a value)).
A backend storage subsystem is a system comprising physical storage devices (e.g., disk array), a disk array controller, a cache memory, mirrored storage devices
(i.e., a primary storage device and its mirrored secondary storage device) under a protocol (e.g., PPRC), and an interface to a virtualization storage appliance. The storage virtualization appliance is a system that contains no physical storage device but provides virtualization (i.e., a plurality of physical storage devices are appeared as a single logical storage unit) of physical storages to a host device or host application.
There are two traditional solutions to perform a migration of SRC from a backend storage subsystem to a storage virtualization appliance:    1. A first solution with no impact on the host device: The SRC must be stopped at a backend storage subsystem and a new SRC is started at a storage virtualization appliance. This solution involves copying all data from a primary storage device to a secondary storage device. During this copying, the secondary storage device loses data consistency and is thus unusable. (The definition of SRC requires two storage locations (i.e., storage sites). The storage locations are referred to as “Primary” site and “Secondary” site. A host device may exist at the primary site and a storage device at the primary site is both readable and writable. This storage device is referred to as primary storage device. The secondary site contains a secondary storage device that is only writable by the primary storage device at the primary site. This secondary storage device may be presented to a host device as read-only.)    2. A second solution with no impact on data consistency: All I/O requests from host devices must be temporarily stopped, before stopping a SRC at the backend storage subsystem and restarting the SRC at the storage virtualization appliance. This second solution does not involve copying all data from the primary storage device to the secondary storage device at backend subsystem.
Both solutions have problems:    1. For the first solution, data must be re-copied from the primary storage device to the secondary storage device at the backend storage subsystem.            This recopying takes long time, during which time a recent backup data in the secondary storage device is not available.        Performance of a host device will suffer during this recopying.            2. For the second solution, there is temporal service down-time (i.e., a user can not request an I/O service through a host device). The service down-time is not allowable, because most users prefer to have 100% service availability.
Therefore, it would be desirable to provide a method transferring a Synchronous Peer to Peer Remote Copy (SRC) from a backend storage subsystem to a storage virtualization appliance without interrupting a host device and without losing data consistency.